Let \(\Omega\) be open, \(u\in C^2(\Omega)\) harmonic and \(f\in C^2(\mathbb{R})\) convex. Then by a simple calculation follows that \(f\circ u\) is subharmonic .
Let \(\Omega\) be open, \(u\in C^2(\Omega)\) harmonic and \(f\in C^2(\mathbb{R})\) convex. Then by a simple calculation follows that \(f\circ u\) is subharmonic .